It is known that ankle prostheses can be used to restore a certain amount of freedom of movement to the joint of an ankle after the ankle has been damaged totally or partially, e.g., due to impact trauma or to disease.
In particular, it is known that an ankle prosthesis having three implants can be implanted, namely, a talar implant designed to be implanted in or on the talus (anklebone), a tibial implant designed to be implanted in or on the tibia, and an intermediate implant designed to be interposed between the tibial implant and the talar implant.
Generally, the intermediate implant has a large amount of freedom of movement between the other two implants. More particularly, the intermediate implant generally rests in a planar abutment on the tibial implant to allow movement in anteroposterior translation, in mediolateral translation, and in rotation about the medullary axis of the tibia that is substantially perpendicular to the surface of the planar abutment.
Usually, the contact interface between the intermediate implant and the talar implant is a rounded friction surface that is generally cylindrical, spherical, or frustoconical in shape in order to allow the leg to move in plantar flexion and in dorsal flexion relative to the leg.
Although ankle prostheses offer features that are advantageous in terms of movement, the ankle prostheses can be unsuitable for the condition of the patient being treated.
When the patient has already undergone orthopedic treatment limiting the mobility of the ankle, the joint generally suffers from instability due to being weakened by muscle atrophy and/or to tendon laxity. Thus, when, for example, consideration is given to performing arthroplasty (joint replacement) serving to restore joint mobility when the joint has been previously immobilized by arthrodesis (joint fusion), or indeed when it is desired to replace a prosthesis that is an old model and whose movement configuration differs from that of the three-implant prosthesis, suddenly restoring many degrees of freedom that have previously been lost tends to disturb the balance of the patient and exposes the patient to risks of falls, of injuries, and of damage to tissue situated at the joint in question.
Therefore, implementing prior art three-implant prostheses requires patients to undergo a very long period of rehabilitation.
In addition, certain national regulatory requirements prohibit the use of prior art three-implant prostheses.